DMMs are human traders on the floor of the NYSE who are supposed
to "facilitate price discovery during market opens, closes
and during periods of trading imbalances or instability,"
according to the
exchange.

"The DMM model, unique to the NYSE, provides an
irreplaceable safeguard to investors and listed companies and is
proven to lower volatility for individual stocks," NYSE
group president Tom Farley said Tuesday in a
statement.

"This is especially critical during complex
market events, such as IPOs and the start of trading each
day."

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As part of the transaction,GTS will become
the DMM for more than 1,200 listed securities. GTS said in a
statement that "virtually all of the Barclays DMM floor team are
expected to join GTS as part of the transaction."

The NYSE also has so-called supplemental liquidity
providers, which are electronic, high-volume traders that are
incentivized to buy and sell stocks to add liquidity. The
high-speed firms Hudson River Trading, Latour Trading, and
Tradebot Systems are SLPs, along with investment banks like
Goldman Sachs and Bank of America Merrill Lynch.

The NYSE is a relative throwback in that it still uses
human traders to set the price of shares early on. Other
exchanges use computers to do it.

The role of DMM came under scrutiny late last year, when
markets went haywire in late August.One of the
NYSE's biggest rivals, as well as electronic-trading firms that
do business on the exchange, criticized the way it handled the
swings in the market that week.

In a statement, Joseph Mecane, managing director in
the electronic equities and credit products business at Barclays,
said the bank continued to believe in the DMM
model.

"However, with the evolving market structure, we also
believe that a firm specializing in the technology of market
making, such as GTS, is best suited to enhance the NYSE DMM
business," he said.